אֶ֭בֶן מָאֲס֣וּ הַבּוֹנִ֑ים הָ֝יְתָ֗ה לְרֹ֣אשׁ פִּנָּֽה׃
건축자의 버린 돌이 집 모퉁이의 머릿돌이 되었나니
Likutei Halakhot
The monarchy of David and the Messiah are also hinted to in Hallel, as it is brought. Also the other aspect is hinted to in Hallel - meaning that which was explained before, that we have a claim to come and regret and repent, since He Himself, may He be blessed, regrets and says, "Bring atonement for Me." And this is [the meaning of] (Psalms 118:22-23), "The stone that the builders rejected became the cornerstone. This was from the Lord." That is, if it seems wonderous to the penitent, how he merited to be accepted - this is "the stone that the builders rejected became, etc.," meaning the penitent that blemished what he blemished. So that is, "The stone that the builders rejected." They rejected him because of his many blemishes, but now he merited to be the cornerstone. And at first glance, the matter is wonderous! But truly, "this was from the Lord," meaning from God Himself. That is, it was from God Himself, as it were, that repentance is effective. For it came down from Him, may He be blessed, since He Himself, may He be blessed, said, "Bring atonement for Me." Hence we also have a claim to regret and to repent. And this is [the meaning of], "This was from the Lord." That it, as it were, was from God Himself that this happened; that repentance is effective, since He Himself regretted, as mentioned above. Yet "it is wonderous in our eyes," in truth. As, for us, it is truly a wonder how repentance is effective, and how we can have a claim to come before Him with our sins and to regret. However, "This was from the Lord," as mentioned above.
Kedushat Levi
Genesis 21,6. “G’d has made laughter for me.” Sarah realized that if G’d had granted her children in her old age instead of during her child-bearing years, He had multiplied the joy she experienced by this birth. Had she given birth in her younger years the pregnancy and subsequent birth would have been periods of discomfort and pain for her. Now, that she had not become pregnant until she was close to 90 years old, every day of that pregnancy had been filled with joyful expectation, and even the birth itself was not felt by her as an excruciatingly painful experience. Instead of thanking G’d in His capacity as Hashem, as we might have expected, she thanked Him in His capacity as אלוקים, the attribute of Justice, realizing that during all the years she had felt deprived of the joys of motherhood, the attribute of Justice seemingly being applied to her, had enabled her to exult in joy at this time.
This feeling of Sarah is reflected in psalms 118,21:אודך כי עניתני ותהי לי לישועה, “I wish to thank You, for You have afflicted me/answered me. For through my affliction my salvation has come.” The same thought is repeated in a different nuance, when David continues (verse 22) אבן מאסו הבונים היתה לראש פנה, “the stone that the builders rejected has become the cornerstone.” David adds, that it has become clear to him that all of this had been planned by G’d in advance, i.e. (verse 23) מאת ה' היתה זאת היא נפלאת בעינינו, “this is the Lord’s doing; it is marvelous in our eyes.” David too, is aware that it is far more rewarding to experience these blessings from G’d in one’s mature years than in one’s early youth. When a youth experiences all these blessings, he does not even recognize them as blessing bestowed by G’d, but credits them to chance or other circumstances. Having experienced G’d’s salvation at a relatively late stage in one’s life makes one doubly grateful to Hashem, i.e. זה היום עשה ה' נגילה ונשמחה בו, “this is the day that the Lord has made, let us exult and rejoice on it.”
When examining the manner in which G’d shares out His largesse, we must distinguish between two categories of recipients. One category enjoys the material benefits provided by Hashem for what they are worth, i.e. they consider the material part as the essential part, not considering them as a means to an end. The second category of recipients are the sages and the pious people who perceive these “gifts” as proof of the caring supervision exercised by G’d over all of His creatures, and they see in it an encouragement to never forget that there is a benevolent King Who rules over us. This is what David referred to when he said in the above-quoted hymn:זה היום עשה ה' נגילה ונשמחה בו, “this is the day that the Lord has made let us rejoice and be happy in Him.” They see in the word בו at the end of this verse a reference to G’d, not to the day.
This feeling of Sarah is reflected in psalms 118,21:אודך כי עניתני ותהי לי לישועה, “I wish to thank You, for You have afflicted me/answered me. For through my affliction my salvation has come.” The same thought is repeated in a different nuance, when David continues (verse 22) אבן מאסו הבונים היתה לראש פנה, “the stone that the builders rejected has become the cornerstone.” David adds, that it has become clear to him that all of this had been planned by G’d in advance, i.e. (verse 23) מאת ה' היתה זאת היא נפלאת בעינינו, “this is the Lord’s doing; it is marvelous in our eyes.” David too, is aware that it is far more rewarding to experience these blessings from G’d in one’s mature years than in one’s early youth. When a youth experiences all these blessings, he does not even recognize them as blessing bestowed by G’d, but credits them to chance or other circumstances. Having experienced G’d’s salvation at a relatively late stage in one’s life makes one doubly grateful to Hashem, i.e. זה היום עשה ה' נגילה ונשמחה בו, “this is the day that the Lord has made, let us exult and rejoice on it.”
When examining the manner in which G’d shares out His largesse, we must distinguish between two categories of recipients. One category enjoys the material benefits provided by Hashem for what they are worth, i.e. they consider the material part as the essential part, not considering them as a means to an end. The second category of recipients are the sages and the pious people who perceive these “gifts” as proof of the caring supervision exercised by G’d over all of His creatures, and they see in it an encouragement to never forget that there is a benevolent King Who rules over us. This is what David referred to when he said in the above-quoted hymn:זה היום עשה ה' נגילה ונשמחה בו, “this is the day that the Lord has made let us rejoice and be happy in Him.” They see in the word בו at the end of this verse a reference to G’d, not to the day.
Chayei Moharan
Faith is the last in the chain of all the spiritual qualities. Yet it is precisely through faith that one attains all other levels, for faith is “the stone that the builders rejected,” which “became the cornerstone” (Psalms 118:22). Along the same lines, the Rebbe said after teaching the lesson "כִּי מְרַחֲמֵם יְנַהֲגֵם" in Likutey Moharan II, 7 that faith is the last level, yet through faith one can rise to all levels and attain Desire, which is higher than everything else. See there in the Sichos that follow Sippurei Maasiyot (Sichos HaR"an 32) (Likutei Halachos Nedarim, Halachah 4, Ot 16)